For review: Term display helper

[Mark Anthony BROWN]

> 
> On 27-Feb-1998, Waye-Ian CHIEW <wchi at students.cs.mu.OZ.AU> wrote:
> > Hello.
> > 
> > This is the term display helper, which takes univ terms and displays them in a
> > choice of pretty formats.
> > 
> > It is not finished and not really useable;  some critical additions, like
> > the scripting language and the interactive browser, haven't been implemented
> > yet. 
> > 
> > -- Ian!!
> 
> Uh, the scripting language?!?
> 
> Does it make the coffee too?  How about a builtin mail reader? ;-)

Of course it makes coffee.  Why else would it be called critical? ;-) ;-)


> I'm not sure that it would be a good idea to reuse "cd" as the name
> for this command.  Something else might be a better idea.
> Perhaps "goto".

IMO, the analogy with directory trees is a good one.  In particular,
I imagine users would like to be able to refer to both absolute and
relative "pathnames".  If a name is to be reused, "goto" is probably
a less helpful choice.

Still, "cd" means "change directory" so unless you are actually going
to refer to subterms as directories all the time, this acronym may
be misleading.

>      
> > X   quit
> > X      Quits and returns the user-modified visibility tree and
> > X      preferences to the caller.
> > X      
> > X   quit! 
> > X      Quits and returns the original visibility tree and user
> > X      preferences to the caller.

There's not much typographical distance between these two, considering
that one of them saves and exits, while the other forgets changes.

How about:

    done
	Exit with user-modified visibility tree and prefs

    quit
	If no changes have been made, quit and return the original

    quit!
	Quit and return the original, forget any changes

and appropriate abbreviations.


> 
> The name `portray' has an existing meaning in Prolog,
> as the "hook" predicate used by `print'.
> The current plan is to eventually make it mean the same thing in Mercury.
> (Although arguably it might be better to use `print_hook';
> that would allow the use of a consistent convention of
> using `foo_hook' as the hook predicate for `foo'.)
> 
> So it might be better to use a name other than `portray'.
> Unfortunately most of the good ones -- e.g. `print', `write', `display',
> and `format' -- are already taken.  I guess you could use `show'.  Hmm...  
> 
> I guess it might eventually be a good idea to use this code for
> `io__print', so maybe you could call it `print'.

I agree.

> Anyone else have any suggestions/comments about this naming issue?

There seems to be two distinct ways that you would want to output
a term:
	- so that it can be parsed to retrieve the original
	  (guaranteed for _any_ term for which this is possible)

	- so that it looks neat and is convenient for a human to
	  read

It is hard to satisfy both with one predicate (anybody got any ideas?).

io__write already satisfies the first point.  IMHO, 'print' is a
good name for something which places the emphasis on the second
point, which is exactly what the term display library does.


Cheers,
Mark.